Heretofore, as a spatial optical modulation element employing a surface plasmon resonance, an element has been proposed wherein on one side of a prism, a metal layer and an optical functional film made of a material with the refractive index changeable by light irradiation (which may be referred to also as a colorant-containing film) are laminated (e.g. Patent Documents 1 to 6). This element is an element having a structure such that a to-be-modulated light is permitted to enter through the prism and confined or reflected by the metal film, and when it emerges from the prism, a modulation drive light is irradiated to the optical functional film, as the case requires, so that the condition for confining the to-be-modulated light is changed by ON/OFF of the modulation drive light to make high speed optical modulation practically possible.
Patent Document 1: JP-A-5-273503
Patent Document 2: JP-A-2000-292758
Patent Document 3: JP-A-2000-314857
Patent Document 4: JP-A-2000-314859
Patent Document 5: JP-A-2000-314860
Patent Document 6: JP-A-2002-258332